Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy.
In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
However, hybrid vehicles and other low-manifold vacuum vehicles may have limited engine run-time with sufficient manifold vacuum to execute a purging operation. As an alternative, the purged fuel vapors may be directed to engine intake upstream of the throttle body, but this requires a diverter valve to lower local pressure in the engine intake, thereby adding manufacturing costs. Further, the desorption of fuel vapors is an endothermic reaction, the desorption efficiency decreasing as the canister temperature drops. Dedicated heating elements have been used to warm the fuel vapor canister and/or purge air entering the canister, but this again adds manufacturing costs and increases the power demand on the vehicle battery during operation.
The inventors herein have recognized the above problems, and have developed systems and methods to at least partially address them. In one example, a method, comprising: purging fuel vapors from a fuel vapor canister and/or a fuel vapor bleed element to an engine intake with air routed through a transmission bellhousing. In this way, purge air may be warmed by heat generated in the transmission bellhousing during engine operation, thereby increasing desorption efficiency and reducing bleed emissions.
In another example, an engine system, comprising: a fuel vapor canister coupled to a fuel tank; a fuel vapor bleed element coupled to the fuel vapor canister, a purge line coupled between the an engine intake and one or more of the fuel vapor canister and fuel vapor bleed element; a vent line coupled between a transmission bellhousing and one or more of the fuel vapor canister and fuel vapor bleed element; and one or more air inlets coupled between the transmission bellhousing and atmosphere. The transmission bellhousing may be configured to pressurize atmospheric air between a bellhousing wall and a ring gear, and further configured to flow pressurized air to the fuel vapor canister and/or fuel vapor bleed element via the vent line. In this way, purge air may be generated regardless of engine manifold vacuum, allowing for increased opportunities to perform purge operations. This may in turn reduce bleed emissions, as well as increase engine efficiency, as intake vacuum maybe maintained at a low level. Further, a diverter valve may be omitted, decreasing manufacturing costs and system complexity.
In yet another example, a method for purging a fuel vapor canister, comprising: opening a purge valve coupled between the fuel vapor canister and an engine intake; opening a vent valve coupled between the fuel vapor canister and a transmission bellhousing; flowing atmospheric air into the transmission bellhousing via an air filter; transferring heat to the atmospheric air; pressurizing the atmospheric air in the transmission bellhousing between a bellhousing wall and a ring gear; flowing the heated, pressurized atmospheric air to the fuel vapor canister to purge fuel vapor stored in the fuel vapor canister; and flowing the purged fuel vapor to the engine intake. In this way, purge air may be heated without the addition of a dedicated canister heater or purge air heater. This may reduce manufacturing costs, and increase the efficiency of the vehicle engine and battery, as no additional power or voltage needs to be supplied to warm purge air.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.